1. Field of the Invention
The embodiments described herein relate to image processing techniques. In particular, these embodiments relate to reconstructing a color image from data extracted from an imaging array.
2. Related Art
Because of the tri-stimulus nature of human color perception, in reconstructing a color image of a scene it is typically necessary to recover at least three color components (typically red, green, and blue or cyan, magenta, and yellow) for each picture element (pixel) in the image. Ideally, each photodetector in an imaging device would capture co-aligned red, green, and blue data creating a dense color image. This would eliminate the need for color reconstruction. However, such a system is not feasible due to the required complexity of the photodetectors and the amount of data that would have to be extracted from the imaging device. An alternative approach is to have each photodetector gather data for a single color creating a sparse color image. A known color filter array (CFA) pattern such as a Bayer pattern as described in U.S. Pat. No. 3,971,065 to Bayer applies such an approach.
Single-sensor electronic cameras employing color filter arrays are widely used for the creation of color imagery. In a color filter array of photodetectors such as the aforementioned Bayer pattern array, each photodetector site (pixel) provides information for a single color. For the color image to be of use it is typically converted to a dense color image having data for all three colors at each pixel location. Typically, a fair amount of image processing circuitry is allocated to the task of converting the sparse image to the dense image via elaborate color interpolation schemes. In such schemes the basic assumption that the missing colors at a given pixel are similar to the corresponding detected colors at neighboring pixels. The neighborhood may be defined in a single linear dimension such as 1xc3x973, 1xc3x975, or 1xc3x977 or may be defined in two dimensions such as 3xc3x973 or 5xc3x975. Then, given the neighborhood, interpolation filters combine the pixels within the neighborhood into a single pixel that will be used for the missing color.
When the color similarity assumption does not hold, as is the case at object boundaries, interpolation generally results in one of two situations, or possibly both. First, the images may become blurry. Second, false colors (color artifacts) may be introduced into the image. For objects with elongated boundaries (e.g. long horizontal edges) the artifacts appear as long stripes of artificial color that tends to draw the viewer""s attention. This is due to the uniformity in the application of the interpolation filters. These situations are then corrected by performing additional image processing. Blurry images may be sharpened via edge enhancement operations and false colors removed through the use of median or low pass filters.
Another drawback to the interpolation approach is the requirement for algorithmic and associated hardware support adding complexity to the system design. Therefore, there is a need for reducing system complexity for achieving color reconstruction while maintaining adequate color reproduction.
An object of an embodiment of the present invention is to provide a simplified method for color reconstruction having reduced processing requirements.
Another object of an embodiment of the present invention is to provide a computationally efficient system and method for improving the quality of color images which are reconstructed from data of multiple color channels of an imaging array.
Another object of an embodiment of the present invention is to provide an improved system and method for reconstructing a color image which minimizes the introduction of artifacts.
It is yet another object of an embodiment of the present invention to provide an improved method of constructing a color image from image data extracted from an imaging array.
Briefly, an embodiment of the present invention is directed to a system and method of processing data associated with an array of pixels where each pixel corresponds with one of a plurality of spectral regions and a value representative of an intensity of photoexposure in that spectral region. At each particular pixel location being associated with a corresponding particular one of the plurality of spectral regions, at least one neighboring pixel is selected. The selected neighboring pixel is associated with a spectral region which is distinct from the particular spectral region. Then, the value representative of the intensity of photoexposure associated with the selected pixel is assigned to the particular pixel location as an estimate of an intensity of photoexposure in the distinct spectral region at the particular pixel location.
By assigning to each pixel location color information extracted from adjacent pixel locations, the processing requirements of color reconstruction remain modest. By properly selecting particular neighboring pixels for providing the missing color information, color artifacts can be minimized at object boundaries in the original scene.